Method of making crack resistant magnetic write head

ABSTRACT

The front edge of the a zero throat height (ZTH) defining insulation layer in a magnetic head is formed with a central portion which is centered with respect to a second pole tip with first and second lateral portions which are on each side of the central portion and parallel to the ABS. The central portion is recessed from the ABS a distance appropriate for defining the ZTH between the first and second pole pieces of the head and the first and second lateral edges are further recessed into the head so as to increase the volume of the overcoat layer between the ABS and the first and second lateral edges. The increased volume of the overcoat layer better absorbs stresses and strains due to shock loading and temperature so as to reduce cracking of the head at the ABS.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.08/731,816 filed Oct. 21, 1996 which is now U.S. Pat. No. 5,880,915.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of making a crack resistantmagnetic write head and more particularly to a method of making a writehead with an enlarged overcoat layer portion adjacent an air bearingsurface (ABS) for absorbing stress arising from impacts and heat.

2. Description of the Related Art

A typical magnetic write head has one or more coil layers embedded in aninsulation stack that is sandwiched between first and second polepieces. The first and second pole pieces are magnetically connected andhave first and second pole tips separated by a magnetically insulativegap layer to form a gap at an air bearing surface (ABS). The coil layerinduces a magnetic field in the pole pieces which fringes across thegap. The magnetic write head is covered with an overcoat layer forprotection of the aforementioned components.

A combined head, such as a merged magnetoresistive (MR) head, includesthe aforementioned write head as a write head portion combined with anMR read head portion. The combined head is carried on a slider that ismounted on a suspension in a magnetic disk drive. The suspension ismounted to an actuator which moves the combined head over selectedtracks on a rotating disk for reading and writing signals thereon. Asthe disk rotates, a cushion of air provides an air bearing between thedisk and the slider which counterbalances the loading force exerted bythe suspension. The ABS, the surface of the slider facing the disk, istypically spaced about 0.075 μm from the disk when the disk rotates.When the rotation commences, the slider takes off from the disk andrides on the cushion of air. When the disk stops, the slider lands onthe disk. This is referred to in the art as contact start and stop (CSS)operation. Friction and heat are developed by both events.

In the fabrication of a thin film magnetic write head it is importantthat zero throat height (ZTH) be accurately located. The ZTH is thepoint after the ABS where the first and second pole pieces separate fromone another. This separation is caused by a central recessed edge of theinsulation stack which elevates the second pole piece above the firstpole piece. It is desirable to locate the ZTH as near the ABS aspossible in order to minimize flux leakage between the pole pieces. Theinsulation stack typically includes a first insulation layer (I1) on thefirst pole piece layer, one or more coil layers on the first insulationlayer, a second insulation layer (I2) over the coil layer and a thirdinsulation layer (I3) over the second insulation layer. One of theseinsulation layers, typically the first insulation layer, has a forwardcentral edge which extends laterally and parallel to the ABS and definesthe ZTH. This central edge is typically located about 1-2 μm from theABS.

A portion of the ABS is formed by front edges of the thin filmcomponents of the write head. These edges comprise the front edge of thegap layer and the front edges of the first and second pole tips. An ABSview of the write head shows a small gap layer end disposed between awide first pole tip end and a narrow second pole tip end. The secondpole tip end appears as a pedestal with first and second side walls thatare parallel to one another and perpendicular to the ABS. The secondpole tip is the trailing pole tip with respect to a rotating disk.Accordingly, the lateral width between the side walls of the second poletip defines the track width of the write head. Surrounding the edges andforming a portion of the ABS is a front edge of the overcoat layer. Theovercoat layer has a wide lateral expanse in both directions from thefirst and second walls of the second pole tip. The overcoat layer alsoextends rearwardly toward the back gap, interfacing with the centraledge of the ZTH-defining insulation layer, which typically is the firstinsulation layer. This interface extends parallel to the ABS alongsubstantially the full lateral width of the front edge of theZTH-defining insulation layer. Since the edge of the ZTH-defininginsulation layer is recessed only 1-2 μm from the ABS, there is anextremely small volume of the overcoat layer between the ABS and theedge of the ZTH-defining insulation layer.

A magnetic write head is a lamination of many components. Unfortunately,these components are fabricated from different materials with differentthermal coefficients of expansion and different moduli of elasticity.Typically, the insulation stack is photoresist, the overcoat layer andthe gap layer are alumina (Al₂O₃), the pole pieces are Permalloy(Ni₇₉Fe₂₁), and the coil layer is copper. The modulus of elasticity ofthe photoresist is 7, as compared to 100 for alumina and 200 forPermalloy. Therefore, relative to the overcoat layer and the polepieces, the insulation stack is very compliant. Further, the coefficientof thermal expansion of photoresist is 36 E-6/degree C., whereas thethermal expansion of the overcoat layer is 6 E-6/degree C. Accordingly,the insulation stack expands 6 times as much as the overcoat layer.

The write head is a delicate structure which, unfortunately, issubjected to impact shock during fabrication, during assembly in a diskdrive, during shipment and during use. Further, the head is subjected toexpansive stress due to heating of the coil. During contact start andstop, the ABS end of the head is subjected to both heat and impactloading. The head components are stressed and strained by theseconditions. The weakest region of the head is the small volume of theovercoat layer between the ABS and the front edge of the ZTH-defininginsulation layer. An alumina overcoat layer absorbs stress well,especially since its modulus of elasticity is reasonably close to thatof the Permalloy pole tips. Unfortunately, the extent of the aluminaovercoat layer between the ABS and the front edge of the ZTH-defininginsulation layer is minimal. Impact loading at the ABS quickly affectsthe insulation stack, which responds like jelly as compared to the otherlayers. Further, when heated, the insulation stack expands more than theovercoat layer, causing additional stresses and strains at allinterfaces with the insulation stack. It would be desirable to increasethe depth of the overcoat layer from the ABS into the head, but this isnot practical because the magnetics of the head would be adverselyaffected by an increase in the ZTH.

Because of the structure and the materials employed, the write headdevelops cracks at the ABS. The weakest point at the ABS is the insidecorners of the second pole tip. Cracks typically radiate from thesecorners and migrate laterally or radiate at some lateral location andmigrate toward these corners. With repeated stress, these cracks grow.This phenomenon and resultant degradation of head performance isreported in IEEE Trans Mag. 31, 2991, 1995 by Chekanov et al.

SUMMARY OF THE INVENTION

The present invention provides an increase in the volume of the overcoatlayer adjacent the ABS without increasing the ZTH. This is accomplishedby recessing first and second portions of the laterally extending edgeof the ZTH-defining insulation layer on each side of the second poletip, leaving a central edge of the insulation layer intact for definingthe ZTH. In a plan view of the thin film surfaces of the head, theZTH-defining insulation layer has a pair of recessed shoulders with aforwardly projecting neck, the neck providing the central edge whichdefines the ZTH. The central edge is maintained at 1-2 μm from the ABS,to define the ZTH, as taught by the prior art, while the lateral edges,which define the shoulders, are recessed from the ABS, on the order of5-6 μm, since they are not needed to define the ZTH. This allows thealumina of the overcoat layer to fill in the space given up by thelateral edges so as to provide an additional volume of the overcoatlayer adjacent the ABS for absorbing stresses and strains from shockloading and heat. Experiments have been conducted to show that writeheads having ZTH-defining insulation layers with recessed first andsecond lateral edges on each side of a central edge which defines theZTH develop significantly less cracks than write heads that do not havethe recessed first and second lateral edges.

A limitation on the amount that the first and second lateral edges ofthe ZTH-defining insulation layer can be recessed is the location of thefront edge of the coil layer. The coil is located as close as possibleto the ABS to minimize magnetic saturation of the thin second pole tip.The front edge of the coil is typically parallel to the ABS for 60-100μm. Accordingly, the first and second lateral edges of the insulationlayer are preferably recessed throughout the lateral expanse of thefront edge of the coil on each side of the central edge of theinsulation layer thereby optimizing the volume of the overcoat layeradjacent the ABS.

An object of the present invention is to minimize cracking at the ABS ofa magnetic write head.

Another object is to increase the volume of the overcoat layer near theABS without increasing the ZTH of a magnetic write head.

A further object is to configure a front edge of a ZTH-defininginsulation layer so that a central portion of the front edge defines theZTH and first and second lateral portions on each side of the centralportion are recessed from the central portion.

Other objects and attendant advantages of the present invention willbecome apparent upon reading the following description taken togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is plan view of a magnetic disk drive.

FIG. 2 is a view taken perpendicular to the plane II—II of FIG. 1.

FIG. 3 is a side view of the magnetic disk drive of FIG. 1.

FIG. 4 is a view taken perpendicular to the plane IV—IV of FIG. 2showing front portions of a write head portion and a read head portionof a prior art head with an overcoat layer in place.

FIG. 5 is an ABS view of the prior art head taken perpendicular to theplane V—V of FIG. 4.

FIG. 6 is a plan view of the write head portion of the prior art head ofFIG. 4 with the overcoat layer removed.

FIG. 7 is an enlarged front portion of the prior art write head of FIG.6 with a front portion of one of the coil layers, the insulation stackand the second pole piece shown in hidden lines under an overcoat layer.

FIG. 8 is a view taken perpendicular to the plane VIII—VIII of FIG. 7.

FIG. 9 is a side elevation view of the present write head taken alongplane IX—IX of FIG. 2 with the overcoat layer in place.

FIG. 10 is an ABS view taken perpendicular to the plane X—X of FIG. 9.

FIG. 11 is a plan view of the present write head with the overcoat layerremoved.

FIG. 12 is an enlarged view of a front portion of the present write headof FIG. 11 with a front portion of one of the coil layers, theinsulation stack and the second pole piece shown in hidden lines underthe overcoat layer.

FIG. 13 is a view taken perpendicular to the plane XIII—XIII of FIG. 12.

FIG. 14 is a chart showing the results of experiments comparing priorart write heads (dashed line) with the present write heads (continuousline).

FIG. 15 is a series of steps involved in making the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals designatelike or similar parts throughout the several views there is illustratedin FIGS. 1, 2 and 3 a magnetic disk drive 30. The drive 30 includes aspindle 32 which supports and rotates a magnetic disk 34. The spindle 32is rotated by a motor 36 which, in turn, is controlled by a motorcontroller 38. A magnetic head 40, which may be a merged MR head forrecording and reading, is mounted on a slider 42 supported by asuspension 43 and actuator arm 44. A plurality of disks, sliders andsuspensions may be employed in a large capacity direct access storagedevice (DASD) as shown in FIG. 3. The suspension 43 and actuator arm 44position the slider 42 to place the magnetic head 40 in a transducingrelationship with a surface of the magnetic disk 34. When the disk 34 isrotated by the motor 36, the slider is supported on a thin (typically,0.075 μm) cushion of air (air bearing) by an air bearing surface (ABS)46 of the slider and the magnetic head. The magnetic head 40 is thenemployed for writing information to multiple circular tracks on thesurface of the disk as well as for reading information therefrom.Processing circuitry 48 exchanges signals representing said informationwith the head 40, providing motor drive signals, and providing controlsignals for moving the slider 42 to various tracks.

FIG. 4 is a side cross-sectional elevation view of a prior art mergedmagnetoresistive (MR) head 50 which has a write head portion 51 and aread head portion 52, the read head portion employing an MR sensor 53.The MR sensor 53 is sandwiched between first and second gap layers 54and 56 and the gap layers are sandwiched between first and second shieldlayers 58 and 60. In response to external magnetic fields, theresistance of the MR sensor 53 changes. A sense current conductedthrough the sensor causes these resistance changes to be manifested aspotential changes. These potential changes are then processed by theprocessing circuitry 48 shown in FIG. 3.

The write head portion of the prior art head includes a coil layer 64which is sandwiched between first and second insulation layers 66 and68. A third insulation layer 70 may be employed for planarizing the headto eliminate ripples in the second insulation layer caused by the coillayer 64. The first, second and third insulation layers are referred toin the art as an “insulation stack”. The coil layer 64, and the first,second and third insulation layers 66, 68 and 70 are sandwiched betweenfirst and second pole piece layers 72 and 74. The first and second polepiece layers 72 and 74 are magnetically coupled at a back gap 76 andhave first and second pole tips 78 and 80 which are separated by a gaplayer 82 at the ABS. As shown in FIG. 2 first and second solderconnections 84 and 86 connect leads (not shown) from the MR sensor 52 toleads (not shown) on the suspension 43 and third and fourth solderconnections 88 and 90 connect leads 92 and 94 from the coil 64 (see FIG.6) to leads (not shown) on the suspension.

The second pole tip 80 of the write head in FIG. 6 has first and secondside walls 96 and 98 which are parallel with respect to one another andperpendicular to the ABS. The second pole piece 74 has a flare point 100which is where the pole piece 74 flares out and forms a yoke portion ofthe pole piece. The coil 64 is located as close as practical to the ABSso as to minimize saturation of the second pole tip 80. The insulationstack, which comprises first, second and third insulation layers 66, 68and 70, as shown in FIG. 4, is also located as close as practical to theABS. The insulation stack defines a zero throat height (ZTH), as shownat 102 in FIG. 4 and at 104 in FIG. 6. The ZTH is the location of thefirst separation of the first and second pole pieces 72 and 74 after theABS. A short ZTH will minimize flux leakage between the first and secondpole pieces. The first insulation layer 66 typically has alaterally-extending front edge 104, as seen in FIG. 6, which defines theZTH between the first and second pole pieces. The edge 104 is typicallyflat so as to correspond with a front flat edge 106 of a front coil ofthe coil layer 64. It should be understood that while the firstinsulation layer is typically the ZTH-defining layer in someembodiments, the second or the third insulation layer may be theZTH-defining layer.

In FIGS. 7 and 8 there is shown an overcoat layer 110 which covers theaforementioned layers of the write head. As shown in FIG. 8, theovercoat layer 110 is very shallow between the ABS and the ZTH forming aslender overcoat volume 112 which extends along the lateral expanse ofthe front flat edge 104 of the first insulation layer 66. The depth D₁of this volume from the ABS to the ZTH is on the order of 1-2 μm.Immediately adjacent this volume is the front edge 104 of the firstinsulation layer 66 which is composed of photoresist. Because of theclose proximity of the front edge 104 to the ABS the first insulationlayer 66, as well as the second and third insulation layers, receiveimpact loading upon contact start and stop of the magnetic head withrespect to the rotating disk. Since the photoresist material has arelatively low modulus of elasticity of 7, it is very compliant andshows a large deformation under a small stress. The overcoat layer 110is typically constructed of a much stiffer material, such as alumina,which has a modulus of elasticity of 100. This modulus of elasticity isrelatively close to the modulus of elasticity of the first and secondpole pieces which is 200 for Permalloy. Another problem with thephotoresist material of the insulation stack is that its coefficient ofthermal expansion is 36 E-6/degree C., whereas the coefficient ofthermal expansion of the alumina overcoat layer is 6 E-6/degree C.Accordingly, the photoresist insulation stack expands six times as muchas the alumina overcoat layer. This expansion exerts a force at theinterfaces of the alumina overcoat layer pushing it toward the ABS witha tendency to separate the overcoat layer from the second pole tip. Heatis caused by friction during contact start and stop and by the one ormore coil layers and leads. Sometimes the cracks develop a step whichprovides a cutting edge at the ABS of the head. When this cutting edgecontacts the surface of a rotating disk, layers of the head can bedelaminated and/or the surface of the disk damaged. It would bedesirable if the depth of the volume 112 could be recessed further intothe head from the ABS, however, this would interfere with the magneticsof the head by changing the ZTH. Because of the very small volume of theovercoat layer at 112 the head develops cracks 114, particularly at theinside corners of the second pole tip, as shown in FIG. 5.

FIGS. 9-13 show details of the present invention. The combined head 120and its write head portion 121 are the same as the prior art except thefront edge of the insulation stack and a corresponding adjacent internaledge of the overcoat layer are reconfigured so as to minimize crackingof the head at the ABS, as shown in FIG. 10. The ABS has a laterallyextending width dimension which extends perpendicularly to the directionof media movement (see FIG. 1) and has a length dimension which extendsparallel to the to the direction of media movement. As shown in FIGS.11-13, the front edge of the specially reconfigured first insulationlayer 122 has a central edge portion 124 and first and second lateraledge portions 126 and 128. The central edge portion 124 encompasses thesecond pole tip and extends laterally with respect to the ABS a shortdistance from both sides of the first and second walls 96 and 98 of thesecond pole tip, as shown in FIGS. 11 and 12. The lateral distance ispreferably in the range of 6-7 μm. If the distance between the sidewalls of the pole tip is on the order of 2 μm, then the total length ofthe front edge 124 is about 12-14 μm. The first and second lateral edges126 and 128 of the first insulation layer 122 extend laterally withrespect to the ABS and parallel to the ABS in both directions from thecentral front edge 124. The lateral edges 126 and 128 are recessedfurther from the ABS than the central edge 124. It should be noted thatthe lateral edges 126 and 128 are substantially flat which correspondsto the flat front edge 106 of the coil layer. The extent of the recesseddistance of each of the lateral edges 126 and 128 is dependent upon therecessed distance of the front edge 106 of the coil layer. The lateraledges 126 and 128 must be located between the ABS and the front edge ofthe coil layer so as to permit complete encapsulation of the coil layerby the insulation stack. The recessed distance D₂ of each of the lateraledges 126 and 128 from the ABS may be on the order of 6-7 μm. Therecessed distance of the central edge 124 may be on the order of 1-2 μm.With this arrangement the central edge 124 defines the ZTH of the headat 1-2 μm and the lateral edges 126 and 128, which are not required todefine the ZTH, are further recessed into the head. The front edge 106of the coil layer may have a lateral expanse on the order of 80 μm.Accordingly, the central edge 124 and the lateral edges 126 and 128preferably have a similar lateral extension of substantially 80 μm.Since the majority of the front edge of the first insulation layer 122has been recessed further into the head, the depth of the volume of thealumina overcoat layer is increased, as shown by D₂ in FIG. 13. Sincealumina is a better shock absorber of impact loading at the ABS crackingof the overcoat layer 110 at the ABS is substantially eliminated, asshown in FIG. 10.

FIG. 14 is a graph showing results of testing write heads with prior artZTH-defining insulation layers as compared to the present inventionwhich reconfigures the front edge of the ZTH-defining insulation layerto accommodate additional alumina of the overcoat layer. It can be seenthat at 300° C., cracking of the head at the ABS is five times morelikely with the prior art head (dashed line) as compared to the presentwrite head (continuous line).

A method of making the present inductive write head is shown in FIG. 15.The ZTH-defining photoresist layer is spun on the first pole piece. Thephotoresist layer is then masked with a mask which has a central frontedge to define the ZTH and first and second lateral front edges whichare recessed from the ZTH. Light is then imaged through the mask ontothe photoresist layer, after which the photoresist layer is developedand hard-baked. After forming the other insulation layers, the overcoatlayer is formed on the ZTH-defining insulation layer providing anincreased volume of the overcoat layer adjacent the ABS for minimizingcracking of the head at the ABS.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

We claim:
 1. A method of making a zero throat height (ZTH) defininginsulation layer that defines a ZTH of a magnetic head wherein the headhas an air bearing surface (ABS) comprising the steps of: spinning a ZTHdefining photoresist layer on a first pole piece layer; masking thephotoresist layer with a mask which defines a central edge recessed froman ABS and oriented parallel to the ABS for forming said ZTH of the headand which defines first and second lateral edges which are furtherrecessed from the ABS and oriented parallel to the ABS; light imagingthe photoresist layer through said mask; developing the photoresistlayer; and hard baking the photoresist layer to form the ZTH defininginsulation layer.
 2. A method as claimed in claim 1, further comprisingthe step of: forming an alumina layer on the ZTH defining insulationlayer.
 3. A method of making a thin film magnetic head with an airbearing surface (ABS) at an end of the head, the ABS having a laterallyextending width dimension which extends perpendicularly to a directionof media movement and a length dimension which extends parallel to saiddirection of media movement, the method comprising: forming a coil layerand an insulation stack with the coil layer embedded in the insulationstack and formed with a laterally extending flat front edge which isrecessed from and parallel to the ABS; forming a gap layer; formingfirst and second pole pieces with first and second pole tipsrespectively that are separated by the gap layer at the ABS, with theinsulation stack sandwiched between the first and second pole pieces andwith the first and second pole pieces magnetically connected at a backgap; forming an overcoat layer covering the coil layer, the insulationstack, the first and second pole pieces and the gap layer; forming thefirst and second pole tips, the gap layer and the overcoat layer withforward surfaces which form a portion of the ABS; forming the insulationstack with a laterally extending, centrally located neck portion betweenthe first and second pole tips with the neck portion having a forwardlylocated, laterally extending central edge recessed from the ABS anddefining a zero throat height and with the insulation stack having firstand second laterally extending lateral edges on each side of the centraledge which are recessed further from the ABS than said central edge andwith said central edge and said first and second lateral edges of theinsulation stack being parallel to the ABS and located between the frontedge of the coil layer and said ABS; and forming the overcoat layer withrecessed edges which interface said central edge and said first andsecond lateral edges of the insulation stack.
 4. A method as claimed inclaim 3 including the steps of: forming a magnetoresistive (MR) stripeand first and second gap layers with the MR stripe sandwiched betweenthe first and second gap layers; and forming the first and second shieldlayers with the first and second gap layers sandwiched between the firstand second shield layers.
 5. A method as claimed in claim 3 wherein theinsulation stack is formed of photoresist and the overcoat layer isformed of alumina.
 6. A method as claimed in claim 3 including the stepsof: forming the second pole tip with first and second side walls whichare perpendicular to the ABS and which are laterally spaced to define atrack width of the write head; and forming said central edge of theinsulation stack so that it extends laterally beyond each of said firstand second side walls of the second pole tip.
 7. A method as claimed inclaim 3 including the steps of: forming the insulation stack with first,second and third insulation layers with the first insulation layerlocated on the first pole piece, the coil layer located on the firstinsulation layer, the second insulation layer located on the coil layerand the third insulation layer located on the second insulation layer;and forming one of the insulation layers with said central edge todefine said zero throat height.
 8. A method as claimed in claim 7wherein said one of the insulation layers is formed as the firstinsulation layer.
 9. A method as claimed in claim 2 wherein the centraledge and the first and second lateral edges of the insulation stack areformed with a combined length which is equal to a length of the frontedge of the coil layer.
 10. A method as claimed in claim 9 wherein theinsulation stack is formed of photoresist and the overcoat layer isformed of alumina.
 11. A method as claimed in claim 10 including thesteps of: forming the second pole tip with first and second side wallswhich are perpendicular to the ABS and which are laterally spaced todefine a track width of the write head; and forming said central edge ofthe insulation stack so that it extends laterally beyond each of saidfirst and second side walls of the second pole tip.
 12. A method asclaimed in claim 11 including the steps of: forming a magnetoresistive(MR) stripe and first and second gap layers with the MR stripe beingsandwiched between the first and second gap layers; and forming firstand second shield layers with the first and second gap layers sandwichedbetween the first and second shield layers.